A conventional axial compressor in a gas turbine engine includes a rotor having a plurality of axially spaced rows of circumferentially spaced rotor blades with axially spaced rows of circumferentially spaced stator vanes disposed upstream of respective ones of the blade rows. The stator vanes are conventionally mounted to a single annular outer casing and extend radially inwardly therefrom.
The compressor outer casing typically includes two 180.degree. half casings each having a pair of axial flanges extending longitudinally parallel to the centerline axis of the compressor. This allows for assembly of the compressor with the two half casings, and attached stator vanes, being positioned over and between the respective blade rows, with the axial flanges then being bolted together for completing assembly.
However, since the outer casing is an axially split member having relatively rigid axial flanges, during operation of the compressor as air is compressed through the various stages thereof, the resulting heat generated therefrom causes circumferential variations in thermal expansion of the compressor components. Since the compressor casing supports both the stator vanes and conventional shrouds surrounding the blade tips, the clearances between the shrouds and blade tips and between the stator vanes and conventional labyrinth seal teeth vary circumferentially and thus adversely affect aerodynamic performance.
The prior art includes double walled compressor casings having a unitary outer case and a circumferentially segmented inner case for providing more uniform circumferential thermal expansion and contraction. However, the use of a unitary outer casing requires special procedures for assembling the compressor which add to the complexity and cost of manufacturing the compressor. Furthermore, the prior art double walled compressor casings utilize various structures, and thusly, have varying effectiveness for reducing circumferential thermal distortion of the casings.